The removal of toxic, corrosive and odorous gases can be accomplished by a number of techniques. These may include wet scrubbing, incineration, and removal via gas-phase air filtration using a variety of dry scrubbing adsorptive, absorptive, and/or chemically impregnated media. As opposed to these other methods, gas-phase air filtration does not require the consumption of large quantities water or fuel. Dry-scrubbing media can be engineered from a number of common adsorbent materials with or without chemical additives for the control of a broad spectrum of gases or tailored for specific gases.
In contrast to the reversible process of physical adsorption, chemical adsorption, also referred to as chemisorption, is the result of chemical reactions on the surface of the media. This process is specific and depends on the physical and chemical nature of both the media and the gases to be removed. Some oxidation reactions can occur spontaneously on the surface of the adsorbent, however, a chemical impregnate is usually added to the media. The impregnate imparts a higher contaminant removal capacity and can lend some degree of specificity. Although some selectivity is apparent in physical adsorption, it can usually be traced to purely physical, rather than chemical, properties. In chemisorption, stronger molecular forces are involved, and the process is generally instantaneous and irreversible.
Undesirable airborne compounds such as hydrogen sulfide, ammonia and formaldehyde occur in a number of environments, where most are primarily responsible for the presence of disagreeable odors or irritating or toxic gases. Such environments include municipal waste treatment facilities, paper mills, petrochemical refining plants, morgues, hospitals, anatomy laboratories, hotel facilities, museums, archives, computer and data storage rooms, and other commercial and industrial facilities.
These undesirable compounds may be bacterial breakdown products of higher organic compounds, or simply byproducts of industrial processes.
Hydrogen sulfide (“H2S”), a colorless, toxic gas with a characteristic odor of rotten eggs, is produced in coal pits, gas wells, sulfur springs and from decaying organic matter containing sulfur. Controlling emissions of this gas, particularly from municipal sewage treatment plants, has long been considered desirable. More recently, protecting electronic apparatus from the corrosive fumes of these compounds has become increasingly important. Furthermore, H2S is flammable.
Ammonia (“NH3”) is also a colorless gas. It possesses a distinctive, pungent odor and is a corrosive, alkaline gas. The gas is produced in animal rooms and nurseries, and its control also has long been considered important.
Formaldehyde (“OCH2”) is a colorless gas with a pungent, suffocating odor. It is present in morgues and anatomy laboratories, and because it is intensely irritating to mucous membranes, its control is necessary.
Attempts have been made to provide solid filtration media for removing the undesirable compounds described above from fluid, or moving, streams, such as gas or vapor streams. Although a variety of impregnated substrates are known for removing undesirable contaminants from fluid streams, these known impregnated substrates are highly selective, that is, each impregnate can treat only a specific type of compound. In applications where several undesirable compounds are present, the air filtration media would either need to have several impregnates included therein or several different air filtration media would need to be used. This results in the currently available media not meeting the needs of various industries.
The residential air quality industry has incorporated an absorbent composition containing two or more absorbent compounds into carpet and window blinds. This absorbent composition attempts to absorb numerous undesirable gaseous compounds that are present in household air, including formaldehyde (from plywood and furniture), organic solvents (from paint, adhesives and wallpaper), gases from insecticides, germicides, agricultural chemicals, and odors from cigarette smoke and pets. This absorbent composition has not, however, been applied to industrial, commercial or residential air filtration media.
Therefore, what is needed is an air filtration media having impregnated thereon a composition capable of absorbing multiple categories of undesirable gases, including hydrogen sulfide, formaldehyde and ammonia.